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Does the area planted to wheat
influence the distribution of
Russian wheat aphid biotypes?
C
hanges in the climatic environment have a significant
impact on agricultural production as well as the suitability of
an area for the production of a specific crop. Climate change
has a direct, but also an indirect impact on crop yield by
affecting the prevalence and distribution of pest insects, diseases
and weeds.
Other factors such as increasing production costs and decreasing
prices for crops influence the type of crop and the area planted
to a specific crop. Not only are there constant changes in the natu-
ral environment, but the agricultural landscape is also changing
all the time. During the past couple of years, the agricultural land-
scape in South Africa, especially in the Free State, has changed
dramatically.
The area utilised for wheat production in South Africa showed a de-
clining trend, decreasing by almost 43% from the 2004/2005 season
and by 6% compared to the 2013/2014 season (SAGL, 2015).
The decrease in wheat cultivation is mainly a result of dryland
wheat producers in the summer rainfall area (Free State), shifting
from wheat to summer crops like maize and soybeans. There are nu-
merous factors influencing this shift, from poor growing conditions
and late rains to increased production costs and low wheat prices.
This has resulted in the fragmentation of wheat ecosystems.
Russian wheat aphid,
Diuraphis noxia
, is a global wheat pest,
which utilises wheat as its main host, with a limited number of
alternative hosts. To date, four Russian wheat aphid biotypes
(RWASA1 - RWASA4) are recognised in South Africa and these were
monitored throughout the wheat production areas of South Africa
from 2010 to 2016.
There has been a steady decline in Russian wheat aphid infesta-
tion of wheat in the summer rainfall region (Free State) during this
period, as shown by the increased percentage fields monitored that
had no Russian wheat aphid infestation (
Graph 1
). The decline of
Russian wheat aphid in these areas can be attributed to the decline
of RWASA1, RWASA2 and RWASA3.
There was a steady increase in RWASA4 over the seasons in
these areas. This biotype, however, is limited to a few areas in the
Eastern Free State. In the winter rainfall region (Western Cape),
however, the percentage of fields with no Russian wheat aphid in-
festation decreased from 2010 to 2016, indicating an increase in
Russian wheat aphid infestation in these areas (Graph 1), notably
by RWASA1.
In the irrigation areas (Northern Cape) the percentage of fields
surveyed with no Russian wheat aphid infestation increased drasti-
cally during 2013 and then decreased gradually from 2014 to 2016
(Graph 1), implying an increased aphid prevalence during recent
times. The main biotype identified in these areas was RWASA1.
There was a decrease in the area planted with wheat in
the summer rainfall area (Free State) over seasons, with a drastic
ON FARM LEVEL
Climate change / Decrease in wheat cultivation
Integrated pest control
DR ASTRID JANKIELSOHN,
ARC-Small Grain, Bethlehem
Graph 1: Percentage of wheat fields not infested by Russian wheat aphid over seasons.